Abstract

We demonstrate cooling of an x-ray transition-edge sensor (TES) using solid-state refrigerators based on normal-metal/insulator/superconductor (NIS) tunnel junctions. We are able to operate the NIS refrigerators at a starting temperature of , which is above the TES transition temperature , and still achieve high quality x-ray spectra with an energy resolution of full width at half maximum at . The maximum cooling achieved by the NIS refrigerators is , from a starting temperature of 300 down to .